Composition for optical materials and use thereof

ABSTRACT

A composition for optical materials is herein disclosed which comprises the following two components (a) and (b): 
     (a) a component containing at least one of poly isocyanates represented by the formula (1) ##STR1## wherein A is an alkanediyl group or an alkanetetrayl group which may contain a sulfur atom, or a dithianetetrayl group, and the alkanediyl group or the alkanetetrayl group may be substituted by a phenyl group; B is a methylene chain represented by .paren open-st.CH 2  .paren close-st. m  (m is an integer of 1 to 4) which may contain a sulfur atom, and B&#39;s may be the same or different; and n is an integer of 2 or 4, and 
     (b) a component containing at least one of polythiols having two or more mercapto groups. The composition is useful to provide optical products such as plastic lenses, filters, substrates for recording media and optical fibers which have a very high refractive index and which are excellent in heat resistance.

This application is a divisional of Application No. 08/550,352, filedOct. 30, 1995, issued as U.S. Pat. No. 5,652,321.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a composition for optical materials anda use thereof. The composition for the optical materials of the presentinvention is a composition useful to provide optical products such asplastic lenses, filters, substrates for recording media and opticalfibers which have a very high refractive index and which are excellentin heat resistance.

2. Prior Art

Plastic lenses are lightweight, less breakable, dyeable and excellent inworkability of cutting, polishing and the like as compared withinorganic lenses to. For these reasons, in recent years, they have beenrapidly spread in the field of optical elements such as eyeglass lensesand camera lenses. However, in order to meet the needs of high fashion,the lenses are required to have decreased center thickness, edgethickness and curvature of the lenses, and in other words, it isnecessary that the lenses are thin on the whole. In view of this point,for resin materials which can be used as the optical materials, a higherrefractive index is demanded.

As the lenses having a high refractive index, there are already knownsulfur-containing polyurethane lenses. For example, the specification ofU.S. Pat. No. 4,775,733 (the publication of Japanese Patent Laid-openNo. 46213/1988) has suggested polyurethane lenses comprising a polymerof a xylylene diisocyanate compound and a polythiol compound, and theselenses have been widely spread as optical lenses such as eyeglasslenses. Furthermore, as other lenses having a high refractive index, forexample, the specification of U.S. Patent No. 5,191,055 (the publicationof Japanese Patent Application Laid-open No. 270859/1990) has suggestedpolyurethane lenses comprising a polymer of 1,2-bis(2-mercaptoethyl)thio!-3-mercaptopropane and a polyisocyanate compound.This resin composition has been recognized to possess a highpracticality, particularly a high refractive index, and therefore, ithas been commercialized by many lens makers.

These polyurethane resins have a high refractive index, but they arepoor in heat resistance as compared with olefin group radicalpolymerization type resins, e.g., DAC (diethylene glycol bisarylcarbonate) resins. Therefore, usually during post processing such as thedyeing or surface coating of the lenses which require thermal processingat about 60° to 90° C., the lenses of the polyurethane resins are easilydeformed, and hence much attention should be paid to a thermalprocessing temperature.

As techniques for improving the heat resistance of these polyurethaneresins, there are known methods described in the publications ofJapanese Patent Application Laid-open Nos. 275901/1990, U.S. Pat. No.5,310,847 (a publication of Japanese Patent Application Laid-open No.56525/1991) and the like. However, the polyurethane resin comprising apolymer of two kinds of aliphatic polythiol compounds and an aromaticpolyisocyanate compound in Japanese Patent Application Laid-open Nos.275901/1990 is improved in heat resistance, but the refractive index ofthis polyurethane resin is as low as about 1.57 to 1.61. Accordingly, itis unavoidably recognized that such a resin loses the advantage of thepolyurethane lenses. Furthermore, also in the specification of U.S. Pat.No. 5,310,847 (a publication of Japanese Patent Application Laid-openNo. 56525/1991), there has been disclosed a method which comprisescombining a specific polythiol having a high sulfur content with apolyisocyanate to improve the heat resistance of the polyurethane resin.In this method, however the, kinds of usable polythiols are limited tocompounds having a low molecular weight and a high sulfur content, andwhat is worse, these low-molecular weight polythiols have a strong foulodor, which makes it difficult to industrially use them.

With regard to eyeglass lens resins, the acquirement of dyeableproperties thereof has heretofore been extremely important to meet theneeds of high fashion. In the polyurethane resin having a highrefractive index, the dyeable properties are incompatible with the heatresistance, and therefore, particularly in the case that thepolyurethane resin is used as the eyeglass lenses, it has been necessaryto regulate the heat resistance of the resin to be used into a suitablerange.

However, the recent development of resin dyeing techniques utilizingvarious carriers has permitted, like the resin having a low heatresistance, the dyeing of the resin having an extremely high heatresistance which has not been dyed by a conventional dyeing method usinga dye singly. Nowadays, there is a tendency that not only the highrefractive index but also a high heat resistance is required for theresin as the optical material.

For the plastic lenses for use in various optical lenses such aseyeglass lenses and for compositions which can be used to manufacturethese lenses, the demand of simultaneously satisfying the high heatresistance and the high refractive index is more and more strong. Theimprovement of the polythiol compound is not enough to achieve thisobject, and a polyisocyanate compound which can realize the high heatresistance and the high refractive index is necessary.

As the polyisocyanate compound and its composition which mainly intendto realize the high refractive index, for example, Japanese PatentApplication Laid-open No. 153302/1990 has disclosed thiocarbamic acidS-alkyl ester lenses obtained by reacting a sulfur-containingpolyisocyanate derivative having a sulfide structure or a disulfidestructure with a polythiol derivative. However, in the case that thepolyurethane lenses are manufactured by the use of this polyisocyanatederivative, the high refractive index can be attained by suitablyselecting a combination of the polyisocyanate derivative with thepolythiol derivative which is a polymerization partner, but theextremely high heat resistance which has recently been required is notso considered.

Moreover, Japanese Patent Application Laid-open No. 65193/1994 hasdisclosed an optical material obtained by polymerizing a mixture of atriisocyanate derivative having a sulfur atom and a polythiolderivative. However, three polymerizable functional groups of thissulfur-containing triisocyanate derivative contribute to the improvementof the heat resistance to some extent, but the content of the sulfuratom which has a high atomic refraction decreases, so that the.disclosed optical material cannot always provide the satisfactory resincomposition from the viewpoint of the refractive index. In particular,the polyisocyanate compound disclosed herein has a long methylene chain,and this chain is a molecular structure which disadvantageouslyfunctions in the points of the heat resistance and the refractive index.Consequently, the disclosed optical material is not sufficient torealize a resin composition having a high refractive index.

As a resin having a high heat resistance and a high refractive index,the publication of Japanese Patent Application Laid-open No. 105677/1993has disclosed an optical material obtained by polymerizing a mixturecomprising a triisocyanate derivative having a dithiolan ring in itsmolecule and a polythiol derivative. Additionally, in Japanese PatentApplication Laid-open No. 159275/1992, there has been disclosed a1,4-dithiane derivative substituted by two isocyanatoalkyl groups.

To obtain a polymer simultaneously satisfying the extremely high heatresistance and refractive index, however, even if either isocyanatederivative of a triisocyanate derivative and a diisocyanate derivativedisclosed herein is used the, kinds of polythiol derivatives which canbe used in combination are inconveniently limited.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a composition foroptical materials comprising a polyisocyanate compound and a polythiolcompound which can provide an optical material having an extremely highrefractive index and an excellent heat resistance.

Another object of the present invention is to provide plastic lenseshaving a high refractive index which can be obtained by polymerizing thecomposition.

A further object of the present invention is to provide a novelsulfur-containing isocyanate for use in the preparation of plasticlenses.

The present inventors have conducted an intense investigation on thebasis of a conception that, in order to solve the above-mentionedproblems, a polyisocyanate having a structure which can simultaneouslysatisfy a structurally high refractive index and heat resistance isnecessary, and the polyisocyanate compound having such physicalproperties is

(1) a polyisocyanate compound capable of minimizing the number ofisocyanate groups which are disadvantageous for the refractive index torealize the high refractive index, and capable of realizing the heatresistance by virtue of a central molecular skeleton or a polythiolderivative which is a polymerization partner, or

(2) a compound obtained by introducing sulfur atoms, for realizing thehigh refractive index, corresponding to the number of isocyanate groupsinto a polyisocyanate derivative having many isocyanate groups andcapable of heightening a crosslink density of a polymer to improve theheat resistance.

As a result, it has been found that as the polyisocyanate compound, bythe use of a polyisocyanate compound obtained by introducing a structurecontaining a large number of chemically stable sulfur atoms into apolyisocyanate compound having minimum isocyanate groups sufficient toform a resin, i.e., two functional groups and/or a polyisocyanatecompound having thioalkyl isocyanate groups sufficient to realize thehigh heat resistance as polymerizable functional group units, lenseshaving an extremely high refractive index and an excellent heatresistance can be obtained. In consequence, the present invention hasbeen completed. That is to say, the present invention is directed to acomposition for optical materials which comprises the following twocomponents (a) and (b):

(a) a component containing at least one polyisocyante represented by thefollowing formula ##STR2## wherein A is an alkanediyl group or analkanetetrayl group which may contain a sulfur atom, or adithianetetrayl group, and the alkanediyl group or the alkanetetraylgroup may be substituted by a phenyl group; B is a methylene chainrepresented by .paren open-st.CH₂ .paren close-st._(m) (m is an integerof 1 to 4) which may contain a sulfur atom, and Bs may be the same ordifferent; and n is an integer of 2 or 4, and

(b) a component containing at least one of polythiols having two or moremercapto groups.

Furthermore, the present invention is also concerned with plastic lenseshaving a high refractive index obtained by polymerizing this compositionfor optical materials.

The composition for optical materials which comprises a diisocyanate ora tetraisocyanate containing a sulfur atom according to the presentinvention is a composition useful to provide optical products such asplastic lenses, filters, substrates for recording media and opticalfibers having a very high refractive index and an excellent heatresistance.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, the present invention will be described in detail.

A diisocyanate compound of n=2 in formula (1) which can be used in thepresent invention has a higher sulfur content as compared with thetriisocyanate derivative having a sulfur atom disclosed in JapanesePatent Application Laid-open No. 65193/1994, and such a diisocyanatecompound is extremely advantageous in point of a refractive index.Furthermore, the heat resistance of a resin composition prepared fromthis diisocyanate compound can be obtained by suitably modifying themolecular structure of the isocyanate, or suitably selecting a polythiolcompound which is a polymerization partner.

The preferable diisocyanate compound is a polyisocyanate represented bythe following formula (2):

    OCN--B--S--X--S--B--NCO                                    (2)

wherein X is a lower alkanediyl group having 1 to 4 carbon atoms whichmay contain a sulfur atom, and this alkanediyl group may be substitutedby a phenyl group; and B is a methylene chain represented by .parenopen-st.CH₂ .paren close-st._(m) (m is an integer of 1 to 4) which maycontain a sulfur atom, and Bs may be the same or different.

Of the compounds represented by the formula (1) which can be used in thepresent invention, a tetraisocyanate compound of n=4 is much moreexcellent in heat resistance as compared with the triisocyanatederivative having a sulfur atom disclosed in Japanese Patent ApplicationLaid-open No. 65193/1994 and the 1,4-dithiane derivative substituted bytwo isocyanate alkyl groups described in Japanese Patent ApplicationLaid-open No. 159275/1992. The preferred tetraisocyanate compound is apolyisocyanate represented by the following formula (3): ##STR3##wherein Y is a lower alkanetetrayl group having 1 to 4 carbon atomswhich may contain a sulfur atom or a dithianetetrayl group.

As the isocyanate compound which can be used in the present invention, atetraisocyanate derivative is more preferable in view of heat resistanceand the ease of manufacturing.

Typical examples of the polyisocyanate represented by formula (1) whichcan be used in the present invention includebis(isocyanatomethylthio)methane,bis(isocyanatomethylthio)methylthiomethane,bis(2-isocyanatoethylthio)methane, bis(3-isocyanatopropylthio)methane,isocyanatomethylthio(2-isocyanatoethylthio)methane,2-isocyanatoethylthio(3-isocyanatopropylthio)methane,bis(isocyanatomethylthio)phenylmethane,bis(2-isocyanatoethylthio)phenylmethane,bis(3-isocyanatopropylthio)phenylmethane,1,2-bis(isocyanatomethylthio)ethane,1,2-bis(2-isocyanatoethylthio)ethane,1-isocyanatomethylthio-2-(2-isocyanatoethylthio)ethane,1-isocyanatoethylthio-2-(3-isocyanatopropylthio)ethane,bis(isocyanatomethylthioethyl) sulfide,tetrakis(isocyanatomethylthio)methane,1,1,2,2-tetrakis(isocyanatomethylthio)ethane,2,2,5,5-tetrakis-(isocyanatomethylthio)-1,4-dithiane and2,2,5,5-tetra-kis(isocyanatomethylthio)-1,3-dithiane.

Above all, preferable examples include bis(isocyanatomethylthio)methane,bis(isocyanatomethylthio)phenylmethane,1,2-bis(isocyanatomethylthio)ethane,1,2-bis(2-isocyanatoethylthio)ethane, bis(isocyanatomethylthioethyl)sulfide, 1,1,2,2-tetrakis(isocyanatomethylthio)ethane and2,2,5,5-tetrakis(isocyanatomethylthio)-1,4-dithiane, and more preferableexamples include bis(isocyanatomethylthio)methane,1,2-bis(isocyanatomethylthio)ethane, and the most preferable example isbis(isocyanatomethylthio)methane.

The above-mentioned component (a) may contain polyisocyanate compoundsother than the polyisocyanates represented by formula (1) for thepurpose of suitably improving the physical properties of the opticalmaterials. In this case, the amount of the polyisocyanate compound to beused represented by formula (1) is 60 mol % or more, preferably 70 mol %or more, more preferably 80 mol % or more of the total polyisocyanates.

Typical examples of the polyisocyanate compound other than thepolyisocyanates represented by formula (1) include o-xylylenediisocyanate, m-xylylene diisocyanate, p-xylylene diisocyanate, α, α,α', α'-tetramethyl-p-xylylene diisocyanate, α, α,α',α'-tetramethyl-m-xylylene diisocyanate,1,3,5-tris(isocyanatomethyl)benzene, and nuclear chlorides, bromides,methylated compounds and ethylated compounds thereof such as4-chloro-m-xylylene diisocyanate, 4,5-dichloro-m-xylylene diisocyanate,2,3,5,6-tetrabromo-p-xylylene diisocyanate, 4-methyl-m-xylylenediisocyanate, 4-ethyl-m-xylylene diisocyanate, hexamethylenediisocyanate, isophorone diisocyanate, norbornene diisocyanate,methylenebis(cyclohexylisocyanate), bis(isocyanatomethyl)cyclohexane,1,3-dithiolane-4,5-diisocyanate,4,5-bis(isocyanatomethyl)-1,3-dithiolane andtris(isocyanatomethylthio)methane. Some of these polyisocyanatecompounds are now on the market.

The above-mentioned component (b) comprises at least one polythiolhaving two or more mercapto groups. Examples of these polythiols includealiphatic polythiols such as methanedithiol, 1,2-ethanedithiol,1,1-propanedithiol, 1,2-propanedithiol, 1,3-propanedithiol,2,2-propanedithiol, 1,6-hexanedithiol, 1,2,3-propanetrithiol,1,1-cyclohexanedithiol, 1,2-cyclohexanedithiol2,2-dimethylpropane-1,3-dithiol, 3,4-dimethoxybutane-1,2-dithiol,2-methylcyclohexane-2,3-dithiol, bicyclo2.2.1!hepta-exo-cis-2,3-dithiol, 1,1-bis(mercaptomethyl)cyclohexane,bis(2-mercaptoethyl) thiomalate,(2-mercaptoethyl)-2,3-dimercaptosuccinate,2,3-dimercapto-1-propanol-(2-mercaptoacetate),2,3-dimercapto-l-propanol-(3-mercaptopropionate), diethylene glycolbis(2-mercaptoacetate), diethylene glycol bis(3-mercaptopropionate),1,2-dimercaptopropyl methyl ether, 2,3-dimercaptopropyl methyl ether,2,2-bis(mercaptomethyl)-1,3-propanedithiol, bis(2-mercaptoethyl) ether,ethylene glycol bis(2-mercaptoacetate), ethylene glycolbis(3-mercaptopropionate), trimethylolpropane bis(2-mercaptoacetate),trimethylolpropane bis(3-mercaptopropionate), pentaerythritoltetrakis(2-mercaptoacetate), pentaerythritoltetrakis(3-mercaptopropionate),1,2-bis(2-mercaptoethylthio)-3-mercaptopropane and4,8-bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol; aromaticpolythiols such as 1,2-dimercaptobenzene, 1,3-dimercaptobenzene,1,4-dimercaptobenzene, 1,2-bis(mercaptomethyl)benzene,1,3-bis(mercaptomethyl)benzene, 1,4-bis(mercaptomethyl)benzene,1,2-bis(mercaptoethyl)benzene, 1,3-bis(mercaptoethyl)benzene,1,4-bis(mercaptoethyl)benzene, 1,2-bis(mercaptomethyleneoxy)benzene,1,3-bis(mercaptomethyleneoxy)benzene,1,4-bis(mercaptomethyleneoxy)benzene,1,2-bis(mercaptoethyleneoxy)benzene,1,3-bis(mercaptoethyleneoxy)benzene,1,4-bis(mercaptoethyleneoxy)benzene, 1,2,3-trimercaptobenzene,1,2,4-trimercaptobenzene, 1,3,5-trimercaptobenzene,1,2,3-tris(mercaptomethyl)benzene, 1,2,4-tris(mercaptomethyl)benzene,1,3,5-tris(mercaptomethyl)benzene, 1,2,3-tris(mercaptoethyl)benzene,1,2,4-tris(mercaptoethyl)benzene, 1,3,5-tris(mercaptoethyl)benzene,1,2,3-tris(mercaptomethyleneoxy)benzene,1,2,4-tris(mercaptomethyleneoxy)benzene,1,3,5-tris(mercaptomethyleneoxy)benzene,1,2,3-tris(mercaptoethyleneoxy)benzene,1,2,4-tris(mercaptoethyleneoxy)benzene,1,3,5-tris(mercaptoethyleneoxy)benzene, 1,2,3,4-tetramercaptobenzene,1,2,3,5-tetramercaptobenzene, 1,2,4,5-tetramercaptobenzene,1,2,3,4-tetrakis(mercaptomethyl)benzene,1,2,3,5-tetrakis(mercaptomethyl)benzene,1,2,4,5-tetrakis(mercaptomethyl)benzene,1,2,3,4-tetrakis-(mercaptoethyl)benzene,1,2,3,5-tetrakis(mercaptoethyl)benzene,1,2,4,5-tetrakis(mercaptoethyl)benzene,1,2,3,4-tetrakis(mercaptomethyleneoxy)benzene,1,2,3,5-tetrakis(mercaptomethyleneoxy)benzene,1,2,4,5-tetrakis(mercaptomethyleneoxy)benzene,1,2,3,4-tetrakis-(mercaptoethyleneoxy)benzene,1,2,3,5-tetrakis(mercaptoethyleneoxy)benzene,1,2,4,5-tetrakis(mercaptoethyleneoxy)benzene, 2,2'-dimercaptobiphenyl,4,4'-dimercaptobiphenyl, 4,4'-dimercaptobibenzyl, 2,5-toluenedithiol,3,4-toluenedithiol, 1,4-naphthalenedithiol, 1,5-naphthalenedithiol,2,6-naphthalenedithiol, 2,7-naphthalenedithiol,2,4-dimethylbenzene-1,3-dithiol, 4,5-dimethylbenzene-1,3-dithiol,9,10-anthracenedimethanethiol,1,3-di(p-methoxyphenyl)propane-2,2-dithiol,1,3-diphenylpropane-2,2-dithiol, phenylmethane-1,1-dithiol and2,4-di(p-mercaptophenyl)pentane; polythiols containing heterocyclic ringsuch as 2-methylamino-4,6-dithiol-sym-triazine,2-ethylamino-4,6-dithol-sym-triazine, 2-amino-4,6- dithiol-sym-triazine,2-morpholino-4,6-dithiol-sym-triazine,2-cyclohexylamino-4,6-dithiol-sym-triazine,2-methoxy-4,6-dithiol-sym-triazine, 2-phenoxy-4,6-dithiol-sym-triazine,2-thiobenzeneoxy-4,6-dithiol-sym-triazine,2-thiobutyloxy-4,6-dithiol-sym-triazine and2,5-bis(mercaptomethyl)-1,4-dithiane; aromatic polythiols containing asulfur atom in addition to the mercapto group such as1,2-bis(mercaptomethylthio)benzene, 1,3-bis(mercaptomethyl-thio)benzene,1,4-bis(mercaptomethylthio)benzene, 1,2-bis(mercaptoethylthio)benzene,1,3-bis(mercaptoethylthio)benzene, 1,4-bis(mercaptoethylthio)benzene,1,2,3-tris(mercaptomethylthio)benzene,1,2,4-tris(mercaptomethylthio)-benzene,1,3,5-tris(mercaptomethylthio)benzene,1,2,3-tris(mercaptoethylthio)benzene,1,2,4-tris(mercapto-ethylthio)benzene,1,3,5-tris(mercaptoethylthio)benzene,1,2,3,4-tetrakis(mercaptomethylthio)benzene,1,2,3,5-tetrakis(mercaptomethylthio)benzene,1,2,4,5-tetrakis(mercaptomethylthio)benzene,1,2,3,4-tetrakis(mercaptoethylthio)benzene,1,2,4,5-tetrakis(mercaptoethylthio)benzene and these compounds having analkylated nucleus; aliphatic polythiols having a sulfur atom in additionto the mercapto group such as bis(mercaptomethyl) sulfide,bis(mercaptoethyl) sulfide, bis(mercaptopropyl) sulfide,bis(mercaptomethylthio)methane, bis(2-mercaptoethylthio)methane,bis(3-mercaptopropylthio)methane, 1,2-bis(mercaptomethylthio)ethane,1,2-bis(2-mercaptoethylthio)ethane, 1,2-bis(3-mercaptopropylthio)ethane,1,3-bis(mercaptomethylthio)propane, 1,3-bis(2-mercaptoethylthio)propane,1,3-bis(3-mercaptopropylthio)propane,1,2,3-tris(mercaptomethylthio)propane,1,2,3-tris(2-mercaptoethylthio)propane,1,2,3-tris(3-mercaptopropylthio)propane,tetrakis(mercaptomethylthiomethyl)methane,tetrakis(2-mercaptoethylthiomethyl)methane,tetrakis(3-mercaptopropylthiomethyl)methane, bis(2,3-dimercaptopropyl)sulfide, 2,5-dimercapto-1,4-dithiane, thioglycolates andmercaptopropionates thereof, hydroxymethyl sulfidebis(2-mercaptoacetate), hydroxymethyl sulfide bis(3-mercaptopropionate),hydroxyethyl sulfide (2-mercaptoacetate), hydroxyethyl sulfidebis(3-mercaptopropionate), hydroxypropyl sulfide bis(2-mercaptoacetate),hydroxypropyl sulfide bis(3-mercaptopropionate), 2-mercaptoethyl etherbis(2-mercaptoacetate), 2-mercaptoethyl ether bis(3-mercaptopropionate),1,4-dithiane-2,5-diol bis(2-mercaptoacetate), 1,4-dithiane-2,5-diolbis(3-mercaptopropionate), bis(2-mercaptoethyl) thiodiglycolate,bis(2-mercaptoethyl) thiodipropionate, bis(2-mercaptoethyl)4,4-thiodibutylate, bis(2-mercaptoethyl) dithiodiglcolate,bis(2-mercaptoethyl) dithiodipropionate, bis(2-mercaptoethyl)4,4-dithiodibutylate, bis(2,3-dimercaptopropyl) thiodiglycolate,bis(2,3-dimercaptopropyl) thiodipropionate, bis(2,3-dimercaptopropyl)dithioglycolate and bis(2,3-dimercaptopropyl) dithiodipropionate; andheterocyclic compounds having a sulfur atom in addition to the mercaptogroup such as 3,4-thiophenedithiol and 2,5-dimercapto-1,3,4-thiadiazole.Furthermore, these polythiols which are substituted by halogens such aschlorine and bromine may also be used. They may be used singly or as amixture of two or more thereof.

Of these polythiols, preferable are2,2-bis(mercaptomethyl)-1,3-propanedithiol,1,2-bis(2-mercaptoethylthio)-3-mercaptopropane,4,8-bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol and1,2,4-tris(mercaptomethyl)benzene.

Some of the polyisocyanates represented by formula (1) can be preparedby known methods. For example, bis(isocyanatomethylthio)methane and1,2-bis(isocyanatomethylthio)ethane can be prepared by a methoddescribed in J. Prakt. Chem., 335, p. 294-296 (1993).Bis(isocyanatomethylthio)methane can be obtained by reactingbis(hydrazinocarbonylmethylthio)methane with sodium nitrite in dilutedhydrochloric acid, and then carrying out Curtius rearrangement in hotbenzene. 1,2-Bis(isocyanatomethylthio)ethane can also be prepared in thesame manner.

Furthermore, bis(hydrazinocarbonylmethylthio)methane can be obtained bytreating easily commercially available methylenebisthioglycolic acid inaccordance with a process described in GB 1129085, i.e., by reactingmethylenebisthioglycolic acid with ethanol in the presence of an acidcatalyst under heating reflux to form a bisethyl ester derivative, andfurther reacting this bisethyl ester derivative with hydrazine hydrateunder ice cooling.

Of the isocyanate compounds suitable for component (a) in thecomposition for the optical materials of the present invention, thepolyisocyanate compounds represented by the following formula (4) arenovel compounds: ##STR4## wherein Z is any one of the following groups;--CH₂ CH₂ --, --CH₂ CH₂ SCH₂ CH₂ --, ##STR5## B' is --CH₂ -- or --CH₂CH₂ --; and n is an integer of 2 or 4, with the proviso that when Z is--CH₂ CH₂ --, B' is --CH₂ CH₂ --.

Next, the preparation procedure of a novel isocyanate compound will bedescribed.

1,2-Bis(2-isocyanatoethylthio)ethane represented by the followingformula (5):

    OCNCH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 NCO(5)

can be prepared from easily commercially availableethylenebis(thiopropionic acid) in accordance with the followingprocedure.

In the first place, ethylenebis(thiopropionic acid) is reacted with alower alcohol in the presence of a suitable acid catalyst to beconverted into an ester derivative. As the acid catalyst, sulfuric acid,hydrochloric acid, p-toluenesulfonic acid or the like can be used, andas the lower alcohol, methanol, ethanol, propanol or the like can beexemplified. The reaction may be carried out, utilizing the used alcoholas a solvent, or in a solvent such as toluene or benzene. Water formedduring the reaction may be removed by the use of a dehydrating agentsuch as anhydrous sodium sulfate or molecular sieves, or may besubjected to azeotropic dehydration using a Dean Stark device in asolvent such as toluene. The reaction is practicable between roomtemperature and the boiling point of the solvent, but it is desirable tocarry out the reaction under reflux.

The thus obtained bisester derivative is then reacted with hydrazinehydrate, thereby obtaining 1,2-bis(2-hydrazinocarbonylethylthio)ethane.

At this time, as a reaction solvent, any of methanol, ethanol, propanol,butanol, THF, dioxane and water can be used, but it is desirable to usea lower alcohol in which the bisester derivative as the raw materialdissolves and the product precipitates. With regard to a reactiontemperature, the reaction can be preferably accomplished between 0° C.and the boiling point of the solvent, but it is desirable to carry outthe reaction at room temperature or less. Next,1,2-bis(2-hydrazinocarbonylethylthio)ethane is reacted with a nitrite ina dilute acid, and then subjected to Curtius rearrangement under heatingconditions to obtain 1,2-bis(2-isocyanatoethylthio)ethane. As the diluteacid, an aqueous dilute hydrochloric acid solution or an aqueous dilutesulfuric acid solution can be used, and this dilute acid can also beused together with a solvent which does not disturb the reaction. Noparticular restriction is put on a reaction temperature, so far as itdoes not bring about the Curtius rearrangement reaction, but it ispreferably in the range of 0° to 10° C.

No particular restriction is put on the solvent for the Curtiusrearrangement, so far as it does not react with the product, butpreferable are benzene and toluene. The reaction is practicable at anoptional temperature between room temperature and the boiling point ofthe solvent.

Bis 2-(isocyanatomethylthio)ethyl! sulfide represented by the followingformula (6) can be prepared as follows:

    OCNCH.sub.2 SCH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 SCH.sub.2 NCO(6)

For example, bis(2-mercaptoethyl) sulfide which is easily commerciallyavailable is reacted with a halogenated lower alkyl acetate in thepresence of a base to obtain bis(2-alkyloxycarbonylmethylthioethyl)sulfide. Examples of the usable base include potassium hydroxide, sodiumhydroxide, potassium carbonate and tri-ethylamine. No particularrestriction is put on the solvent, so far as it does not disturb thereaction, but examples of the preferable solvent include water, ethanol,methyl ethyl ketone and methyl isobutyl ketone. The thus obtainedbis(2-alkyloxycarbonylmethylthioethyl) sulfide may be purified singly ormay be directly fed to a subsequent reaction.

Next, the bis(2-alkyloxycarbonylmethylthioethyl) sulfide is reacted withhydrazine hydrate to obtain bis(2-hydrazinocarbonylmethylthioethyl)sulfide. At this time, methanol, ethanol, propanol, butanol, THF,dioxane, water or the like can be used as a reaction solvent, but theemployment of a lower alcohol is desirable. The reaction can be carriedout between 0° C. and the boiling point of the solvent, but it isdesirable to do the reaction at a temperature between 3° C. and roomtemperature.

Furthermore, this bis(2-hydrazinocarbonylmethylthioethyl) sulfide can bereacted with a nitrite in a dilute acid, followed by Curtiusrearrangement under heating conditions, thereby obtaining bis2-(isocyanatomethylthio)ethyl sulfide.

Here, as the dilute acid, an aqueous dilute hydrochloric acid solutionor an aqueous dilute sulfuric acid solution can be used, and this diluteacid can also be used together with a solvent which does not disturb thereaction. No particular restriction is put on a reaction temperature, sofar as it does not bring about the Curtius rearrangement reaction, butit is preferably in the range of 0° to 10° C. No particular restrictionis put on the solvent for the Curtius rearrangement, so far as it doesnot react with the product, but preferable are benzene and toluene. Thereaction is practicable at an optional temperature between roomtemperature and the boiling point of the solvent.

Bis(isocyanatomethylthio)phenylmethane represented by the followingformula (7) can be prepared by the undermentioned procedure: ##STR6##

For example, a lower alkyl thioglycolate is reacted with benzaldehyde inthe presence of an acid catalyst to obtain a lower alkyl(benzylidenedithio)diacetate derivative. Next, the thus obtainedderivative is reacted with hydrazine hydrate to obtain(benzylidenedithio) bis(hydrazinocarbonylmethane). However, theabove-mentioned lower alkyl (benzylidenedithio)diacetate derivative maybe purified singly or may be directly fed to the subsequent reaction. Asa reaction solvent, any of methanol, ethanol, propanol, butanol, THF,dioxane, water and the like can be used, but the employment of a loweralcohol is desirable. The reaction can be carried out between 0° C. andthe boiling point of the solvent, but it is desirable to do the reactionat a temperature between 3° C. and room temperature.

Furthermore, this (benzylidenedithio) bis(hydrazinocarbonylmethane) canbe reacted with a nitrite in a dilute acid, followed by Curtiusrearrangement under heating conditions, thereby obtainingbis(isocyanatomethylthio)phenylmethane. As the dilute acid, an aqueousdilute hydrochloric acid solution or an aqueous dilute sulfuric acidsolution can be used, and this dilute acid can also be used togetherwith a solvent which does not disturb the reaction. No particularrestriction is put on a reaction temperature, so far as it does notbring about the Curtius rearrangement reaction, but it is preferably inthe range of 0° to 10° C. No particular restriction is put on thesolvent. for the Curtius rearrangement, so far as it does not react withthe product, but preferable are benzene and toluene. The reaction ispracticable at an optional temperature between room temperature and theboiling point of the solvent.1,1,2,2-Tetrakis(isocyanatomethylthio)ethane represented by thefollowing formula (8) can be prepared as follows: ##STR7##

For example, easily commercially availableethanediiridenetetrakisthioacetic acid is converted into a tetrakislower alkyl ester derivative with a suitable lower alkyl esterifyingagent.

At this time, the esterification can be carried out by the use of anacid catalyst such as p-toluene-sulfonic acid, sulfuric acid orhydrochloric acid and a lower alcohol, a dialkyl sulfate, diazomethane,an alkyl iodide or the like, but the employment of the acid catalyst andthe lower alcohol or diazomethane is desirable. In the reaction, asolvent such as ethyl ether or a lower alcohol which does not disturbthe reaction can be optionally used.

Next, this tetrakis ester derivative is reacted with hydrazine hydrateto obtain 1,1,2,2-tetrakis-(hydrazinocarbonylmethylthio)ethane. At thistime, as a reaction solvent, any of methanol, ethanol, propanol,butanol, THF, dioxane, water and the like can be used, but it isdesirable to use a lower alcohol in which the tetrakis ester derivativeas the raw material dissolves and the product precipitates. The reactioncan be carried out between 0° C. and the boiling point of the solvent,but it is desirable to do the reaction at a temperature of roomtemperature or less.

Furthermore, this 1,1,2,2-tetrakis(hydrazinocarbonylmethylthio)ethanecan be reacted with a nitrite in a dilute acid, followed by Curtiusrearrangement under heating conditions, thereby obtaining1,1,2,2-tetrakis(isocyanatomethylthio)ethane. In the reaction with thenitrite, as the dilute acid, an aqueous dilute hydrochloric acidsolution or an aqueous dilute sulfuric acid solution can be used, andthis dilute acid can also be used together with a solvent which does notdisturb the reaction. No particular restriction is put on a reactiontemperature, so far as it does not bring about the Curtius rearrangementreaction, but it is preferably in the range of 0° to 10° C.

No particular restriction is put on the solvent for the Curtiusrearrangement, so far as it does not react with the product, butpreferable are benzene and toluene. The reaction is practicable at anoptional temperature between room temperature and the boiling point ofthe solvent. 2,2,5,5-Tetrakis(isocyanatomethylthio)-1,4- dithianerepresented by the following formula (9) can be prepared in the samemanner as above: ##STR8##

That is to say, in accordance with A. Schoberl et al., Ann. Chem., 595,p. 101 (1955), thioglycolic acid is condensed in the presence of ahydrochloric acid catalyst to form2,2,5,5-tetrakis(carboxymethylthio)-1,4-dithiane, and this product isthen converted into a tetrakis lower alkyl ester derivative with asuitable lower alkyl esterifying agent. The esterification can becarried out by the use of a moderate acid catalyst, a lower alcohol, adialkyl sulfate, diazomethane, an alkyl iodide or the like, but theemployment of the acid catalyst and the lower alcohol or diazomethane isdesirable. In the reaction, a solvent such as toluene, benzene or alower alcohol which does not disturb the reaction can be optionallyused.

Next, this tetrakis ester derivative is reacted with hydrazine hydrateto obtain 2,2,5,5-tetrakis(hydrazinocarbonylmethylthio)-1,4-dithiane. Atthis time, as a reaction solvent, any of methanol, ethanol, propanol,butanol, THF, dioxane, water and the like can be used, but theemployment of a lower alcohol is preferable. The reaction can be carriedout between 0° C. and the boiling point of the solvent, but it isdesirable to do the reaction at a temperature of room temperature orless.

Furthermore, this2,2,5,5-tetrakis(hydrazinocarbonylmethylthio)-1,4-dithiane can bereacted with a nitrite in a dilute acid, followed by Curtiusrearrangement under heating conditions, thereby obtaining2,2,5,5-tetrakis(isocyanatomethylthio)-1,4-dithiane.

In the reaction with the nitrite, as the dilute an aqueous dilutesulfuric acid solution can be used, and this dilute acid can also beused together with a solvent which does not disturb the reaction. Noparticular restriction is put on a reaction temperature, so far as itdoes not bring about the Curtius rearrangement reaction, but it ispreferably in the range of 0° to 10° C.

No particular restriction is put on the solvent for the Curtiusrearrangement, so far as it does not react with the product, butpreferable are benzene and toluene. The reaction is practicable at anoptional temperature between room temperature and the boiling point ofthe solvent.

The ratio of the respective components in the composition of the presentinvention, i.e., the ratio of the component (a) to the component (b) isin the range of 0.5 to 1.5, preferably 0.6 to 1.4, more preferably 0.7to 1.3 in terms of NCO/SH ratio.

To the composition of the present invention, some additives may besuitably added if necessary, and examples of the additives include apolymerization catalyst for accelerating a polymerization reaction, anultraviolet light absorber, an antioxidant, a coloring inhibitor, afluorescent dye, a light stabilizer and an oil-soluble dye for theimprovement of weathering resistance. Furthermore, as needed, aninternal releasing agent may also be added thereto.

The lenses of the present invention can be obtained by adding, ifnecessary, a polymerization catalyst and some additives to thecomposition containing the components (a) and (b) of the presentinvention, sufficiently defoaming the mixture, and then carrying out aknown cast polymerization, i.e., pouring a mixed solution into a moldcomprising the combination of a glass mold or a metallic mold and aresin gasket, heating and curing the same. At this time, in order tofacilitate the release of a molded resin from the mold, a releasetreatment may be given to the mold.

The polymerization temperature and the polymerization time in the castpolymerization depend upon the composition of the monomers, the kindsand amounts of additives, but they are such that heating is begun from atemperature of 5° to 20° C. and up to a temperature of about 100° to130° C. is reached in a period of 8 to 30 hours.

In order to accomplish the prevention of reflection, the increase ofhardness, the improvement of wear resistance and chemical resistance,the impartment of fog resistance and fashion sense, and the like, thelenses obtained by the present invention, if necessary, can be subjectedto a physical or a chemical treatment such as surface polishing, anantistatic treatment, a hard coating treatment, a nonreflective coatingtreatment, a dyeing treatment or a dimming treatment.

The lenses obtained by the present invention can be easily dyed in wateror a solvent by the use of a usual disperse dye. At the time of thedyeing, a carrier which is a dyeing assistant may be added to a dye bathin order to facilitate the dyeing.

The sulfur-containing urethane resin obtained by curing the compositionof the present invention has an extremely low dispersibility, a highrefractive index and a low water absorption, is colorless, transparentand lightweight, and is excellent in heat resistance, weatherresistance, impact resistance and surface hardness. Accordingly, theurethane resin is suitable for materials of optical elements such aseyeglass lenses and camera lenses, glazing materials, coating materials,and materials of adhesives.

Next, the present invention will be described in more detail withreference to examples, but the scope of the present invention should notbe limited to these examples at all. In the examples, part and partsmean part by weight and parts by weight, respectively. The performanceof obtained lenses was evaluated by the following tests.

Refractive index and Abbe's number

They were measured at 20° C. by the use of a Pulfrich refractometer.

Appearance

Coloring and transparency were observed with the naked eye.

Heat resistance

A load of 5 g was applied to each test piece by the use of athermomechanical analyzer, TAS300 (made by Rigaku Denki Co., Ltd.), andthen heated at 2.5° C./min. Afterward, a heat deformation starttemperature was measured.

Dyeability

Each plate having a thickness of 9 mm was immersed and dyed at 95° C.for 5 minutes in each of 5 g/l aqueous dyeing solutions of ML-Yellow,ML-Red and ML-Blue which were disperse dyes for plastic lenses made byMitsui Toatsu Dye Inc. After the dyeing, transmittance was then measuredwithin 400 to 700 nm by the use of a spectrophotometer, U-2000 (Hitachi,Ltd.). As total evaluation, a sample having a good dyeability wasrepresented by "o", and a sample having a poor dyeability or nodyeability was represented by "x".

Heat resistance of dye

Each sample lens was immersed in a dye bath at 95° C. for 5 minutes, andit was then visually observed whether or not the lens was deformed.

Water absorption

Each test piece was prepared in accordance with JIS-K-7209, and thenimmersed in water for 48 hours. Afterward, a weight change wascalculated to determine the water absorption.

Surface hardness

A pencil hardness was measured by the use of a pencil scratching testerfor coating of JIS-K-5401.

EXAMPLE 1 Preparation of 1,2-bis(isocyanatoethylthio)ethane!

In a mixed solvent of 150 ml of toluene and 300 ml of ethanol wasdissolved 25 g of commercially available ethylenebis(thiopropionicacid), and one drop of concentrated sulfuric acid was then addedthereto. Next, reaction was carried out for 4 hours under heatingreflux, while dehydration was done by molecular sieves (4A).

The reaction solution was cooled to room temperature, and most ofethanol was then distilled off by an evaporator. Next, the solution waswashed with 50 ml of a saturated sodium hydrogencarbonate solutiontwice, and then dried over anhydrous sodium sulfate. Afterward, thesolution was concentrated under reduced pressure to obtain light yellowoily crude ethylenebis(ethyl thiopropionate).

This compound was dissolved in 50 ml of ethanol, and 12.2 g of hydrazinemonohydrate was added dropwise thereto, while a solution temperature of5° C. was maintained. After 2 hours, the produced white crystalline1,2-bis(hydrazinocarbonylethylthio)ethane was collected by filtration.Next, the collected crystals were washed with 10 ml of cold ethanoltwice. After drying, the dried material was dissolved in 18 ml of water,and then cooled to 5° C. Afterward, 6.7 g of concentrated hydrochloricacid was added dropwise. Furthermore, a solution obtained by dissolving4.2 g of sodium nitrite in 8 ml of water was added dropwise thereto.After 30 minutes, 30 ml of benzene was added thereto, and the solutionwas then heated up to room temperature, while vigorously stirred. Next,the resulting organic layer was separated, dried over anhydrousmagnesium sulfate, and then added dropwise to 100 ml of benzene at 60°C. gently at such a rate that nitrogen was continuously generated. Afterreaction at this temperature for 3 hours, the solution was cooled toroom temperature, and benzene was then distilled off under reducedpressure. The obtained light yellow oily product was distilled underreduced pressure (145° C./1 mmHg) to obtain 8.6 g of colorless oily1,2-bis(isocyanatoethylthio)ethane.

¹ H-NMR (CDCl₃) δ: 3.02 (bs, 4H), 3.44 (m, 4H), 4.18 (m, 4H)

IR: 2270 cm⁻¹

Example 2 Preparation of bis(isocyanatomethylthio)phenylmethane!

With 13.5 ml of benzaldehyde was mixed with 60 g of ethyl thioglycolate,and 13.5 ml of concentrated hydrochloric acid was added thereto,followed by reaction at room temperature for 2 days. Next, the reactionproduct was poured into 400 g of ice water, extracted with 100 ml ofethyl acetate, washed with water, and then dried over anhydrous sodiumsulfate. Afterward, the solvent was distilled off under reduced pressureto obtain light yellow oily crude lower alkyl(benzylidenedithio)diacetate derivative. Next, this derivative wasdissolved in 50 ml of n-propanol without isolating and purifying it, and14 g of hydrazine monohydrate was added dropwise thereto, while asolution temperature of 5° C. was maintained. After 2 hours, theproduced white crystalline(benzylidenedithio)bis(hydrazinocarbonylmethane) was collected byfiltration. Next, the collected crystals were washed with 10 ml of coldethanol twice. After drying, the dried material was dissolved in 40 mlof water, and then cooled to 5° C. Afterward, 13 g of concentratedhydrochloric acid was added dropwise thereto. Furthermore, a solutionobtained by dissolving 8 g of sodium nitrite in 20 ml of water was addeddropwise thereto.

After 30 minutes, 90 ml of benzene was added thereto, and the solutionwas then heated up to room temperature, while vigorously stirred. Next,the resulting organic layer was separated, dried over anhydrousmagnesium sulfate, and then added dropwise to 200 ml of benzene at 65°C. gently at such a rate that nitrogen was continuously generated. Afterreaction at this temperature for 3 hours, the solution was cooled toroom temperature and the resulting white precipitate was removed byfiltration, and benzene was then distilled off under reduced pressure.The obtained colorless oily product was distilled at 80° C. under areduced pressure of 0.3 mmHg for 2 hours to remove impurities, therebyobtaining the desired bis(isocyanatomethylthio)phenylmethane.

¹ H-NMR (CDCl₃) 67 : 4.42 (m, 4H), 5.04 (s, 1H), 7.28 (m, 5H) IR: 2270cm⁻¹

Example 3 Preparation of bis 2-(isocyanatomethylthio)ethyl! sulfide!

In 360 ml of methyl ethyl ketone was dissolved 27.8 g ofbis(2-mercaptoethyl)sulfide, and the solution was then cooled to 5° C.Next, 32 g of a 45% aqueous sodium hydroxide solution was added dropwisethereto, followed by vigorous stirring. To this solution, 60 g of ethylbromoacetate was added dropwise, and reaction was then carried out atroom temperature for 1 hour. Afterward, 200 ml of ethyl acetate wasadded thereto, and the solution was washed with 50 ml of an aqueoussaturated ammonium chloride solution twice, and then dried overanhydrous sodium sulfate. Afterward, the solvent was distilled off underreduced pressure to obtain 44 g of light yellow oilybis(2-ethyloxycarbonylmethylthioethyl) sulfide. This sulfide wasdissolved in 70 ml of isopropanol, and 18 g of hydrazine monohydrate wasadded dropwise thereto, while a solution temperature of 5° C. wasmaintained. After 2 hours, the produced white crystallinebis(2-hydrazinocarbonylmethylthioethyl) sulfide was collected byfiltration. Next, the collected crystals were washed with 20 ml of coldisopropanol twice and further washed with 10 ml of hexane. After drying,the dried material was dissolved in 150 ml of water and then cooled to5° C., and 25 g of concentrated hydrochloric acid was then addeddropwise thereto. Furthermore, a solution obtained by dissolving 16 g ofsodium nitrite in 50 ml of water was added dropwise thereto. After 30minutes, 150 ml of benzene was added thereto, and the solution was thenheated up to room temperature, while vigorously stirred. Next, theresulting organic layer was separated, and then dried over anhydrousmagnesium sulfate. Afterward, toluene was added thereto for dilution soas to bring the total volume to 500 ml, and the solution was then slowlyheated up to 55° C. to gently carry out reaction so that nitrogen mightbe continuously generated. After the reaction at 70° C. for 3 hours, thesolution was cooled to room temperature and then allowed to standovernight, and the resulting white precipitate was removed byfiltration. Afterward, the solvent was distilled off under reducedpressure. The obtained colorless oily product was distilled at 80° C.under a reduced pressure of 0.3 mmHg for 2 hours to remove impurities,thereby obtaining the desired bis 2-(isocyanatomethylthio)ethyl!sulfide.

¹ H-NMR (CDCl₃) 67 : 2.9-3.3 (m, 8H), 4.23 (m, 4H)

IR: 2270 cm⁻¹

Example 4 Preparation of 1,1,2,2-tetrakis(isocyanatomethylthio)ethane!

In a mixture of 300 ml of ethanol and 150 ml of toluene was dissolved 25g of ethanediiridenetetrakisthioacetic acid, and one drop ofconcentrated sulfuric acid was then added thereto. Next, reaction wascarried out for 6 hours under heating reflux, while dehydration was doneby molecular sieves. After the completion of the reaction, the solutionwas cooled to room temperature, washed with 50 ml of an aqueoussaturated sodium hydrogencarbonate solution twice, and then dried overanhydrous sodium sulfate. Afterward, the solution was concentrated underreduced pressure to obtain light yellow oily crude tetraethylethanediiridenetetrakisthioacetate.

Next, this tetrakis ester derivative was dissolved in 65 ml ofisopropanol, and then cooled to 5° C., and 11.5 g of hydrazinemonohydrate was added dropwise thereto over 2 hours. The resulting whitecrystalline 1,1,2,2-tetrakis(hydrazinocarbonylmethylthio)ethane wascollected by filtration, and then air-dried.

This 1,1,2,2-tetrakis(hydrazinocarbonylmethylthio)ethane was dissolvedin 120 ml of water and then cooled to 5° C., and 25 g of concentratedhydrochloric acid was then added dropwise thereto. Furthermore, asolution obtained by dissolving 16 g of sodium nitrite in 25 ml of waterwas added dropwise thereto. After 2 hours, 120 ml of benzene was addedthereto, and the solution was then heated up to room temperature, whilevigorously stirred. Next, the resulting organic layer was separated, andthen dried over anhydrous magnesium sulfate. Afterward, this benzenesolution was then heated up to 55° C. so slowly that a nitrogen gas wasgently generated. After being heated under reflux for 2 hours, thesolution was allowed to stand overnight at room temperature. Theresulting white precipitate was removed by filtration, and the filtratewas concentrated under reduced pressure. The obtained colorlesstransparent oily product was distilled at 80° C. under 0.3 mmHg toremove low-boiling impurities, thereby obtaining 9.2 g of colorlesstransparent oily 1,1,2,2-tetrakis(isocyanatomethylthio)ethane.

¹ H-NMR (CDCl₃) δ: 3.11 (bs, 2H), 4.29 (m, 8H)

IR: 2270 cm⁻¹

Example 5 Preparation of2,2,5,5-tetrakis(isocyanatomethylthio)-1,4-dithiane!

In accordance with a process described in Ann. Chem. 595, p. 101 (1955),80 g of thioglycolic acid was dissolved in 100 ml of concentratedhydrochloric acid, and a hydrogen chloride gas was then introducedthereinto at 5° C. for 2 hours to saturate the solution therewith. Next,the solution was directly heated up to room temperature and then allowedto stand for 7 days. The resulting white precipitate was collected byfiltration, washed with cold water, and then air-dried. Afterward, thismaterial was suspended in 300 ml of ethanol, and an ethyl ether solutionof diazomethane was then added dropwise thereto until reaction had beencompleted, while the solution was vigorously stirred and observation wasmade by TLC (thin-layer chromatography). Excessive diazomethane wastreated with a trace amount of acetic acid, and the reaction solutionwas then concentrated under reduced pressure to obtain light yellow oily2,2,5,5-tetrakis(carboxymethylthio)-1,4-dithiane.

Next, this tetrakis ester derivative was dissolved in 120 ml ofisopropanol, and 13.2 g of hydrazine monohydrate was added dropwisethereto at 5° C. At this temperature, reaction was carried out for 4hours, and the resulting white crystalline2,2,5,5-tetrakis-(hydrazinocarbonylmethylthio)-1,4-dithiane wascollected by filtration, washed with 30 ml of cold ethanol, and thenair-dried. Furthermore, this2,2,5,5-tetrakis(hydrazinocarbonylmethylthio)-1,4-dithiane was dissolvedin 125 ml of water, and 28 g of concentrated hydrochloric acid was thenadded dropwise thereto, while the solution was cooled on an ice bath.After 30 minutes, a solution obtained by dissolving 17.7 g of sodiumnitrite in 55 ml of water was added dropwise thereto. After reaction wascarried out at this temperature for 4 hours, 150 ml of benzene wasadded, followed by vigorous stirring to separate the resulting benzenesolution. Next, this benzene solution was dried over anhydrous magnesiumsulfate, and then heated up to 55° C. so slowly that a nitrogen gas wasgently generated. After being heated under reflux for 2 hours, thesolution was allowed to stand overnight at room temperature. Theresulting white precipitate was removed by filtration, and the filtratewas then concentrated under reduced pressure. The obtained colorlesstransparent oily product was treated at 80° C. under 0.3 mmHg to removelow-boiling impurities, thereby obtaining 10.5 g of colorlesstransparent oily 2,2,5,5-tetrakis(isocyanatomethylthio)-1,4-dithiane.

¹ H-NMR (CDCl₃) δ: 3.22 (m, 4H), 4.30 (m, 8H)

IR: 2270 cm⁻¹

Example 6

Mixed were 35.3 parts (0.186 mol) of bis(isocyanatomethylthio)methane,26.8 parts (0.124 mol) of 1,2,4-tris(mercaptomethyl)benzene and 0.01% byweight (based on the total amount of the mixture) of dibutyltindilaurate to obtain a uniform solution, and this solution was thensufficiently defoamed. Afterward, the solution was injected into a lensmold comprising a glass mold and a gasket. In succession, the solutionwas slowly heated from 40° C. to 120° C. over 20 hours to achievecuring. After the completion of the polymerization, the molded lens wasslowly cooled, and then taken out from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.69, an Abbe's number ν_(d) of 31 and a heatdeformation start temperature of 112° C. Even when dyed in a dye bath at95° C., the lens was not deformed.

After dyeing, transmittances of the lens were 30% in the case ofML-Yellow, 38% in the case of ML-Red and 48% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.02%, and surface hardness was H.

Example 7

Mixed were 30 parts (0.158 mol) of bis(isocyanatomethylthio)methane and28.9 parts (0.078 mol) of4,8-bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol to obtain auniform solution, and this solution was then sufficiently defoamed.Afterward, the solution was injected into a lens mold comprising a glassmold and a gasket. In succession, the solution was slowly heated from30° C. to 120° C. over 23 hours to achieve curing. After the completionof the polymerization, the molded lens was slowly cooled, and then takenout from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.69, an Abbe's number ν_(d) of 32 and a heatdeformation start temperature of 107° C. Even when dyed in a dye bath at95° C., the lens was not deformed.

After dyeing, transmittances of the lens were 28% in the case ofML-Yellow, 32% in the case of ML-Red and 45% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.01%, and surface hardness was 2H.

Example 8

Mixed were 30 parts (0.158 mol) of bis(isocyanatomethylthio)methane,27.4 parts (0.105 mol) of 1,2-bis(2-mercaptoethylthio)-3-mercaptopropaneand 0.01% by weight (based on the total amount of the mixture) ofdibutyltin dilaurate to obtain a uniform solution, and this solution wasthen sufficiently defoamed. Afterward, the solution was injected into alens mold comprising a glass mold and a gasket. In succession, thesolution was slowly heated from 30° C. to 120° C. over 23 hours toachieve curing. After the completion of the polymerization, the moldedlens was slowly cooled, and then taken out from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.68, an Abbe's number ν_(d) of 32 and a heatdeformation start temperature of 100° C. Even when dyed in a dye bath at95° C., the lens was not deformed.

After dyeing, transmittances of the lens were 33% in the case ofML-Yellow, 33% in the case of ML-Red and 41% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.02%, and surface hardness was H.

Example 9

Mixed were 30 parts (0.158 mol) of bis(isocyanatomethylthio)methane and15.8 parts (0.079 mol) of 2,2-bis(mercaptomethyl)-1,3-propanedithiol toobtain a uniform solution, and this solution was then sufficientlydefoamed. Afterward, the solution was injected into a lens moldcomprising a glass mold and a gasket. In succession, the solution wasslowly heated from 30° C. to 120° C. over 23 hours to achieve curing.After the completion of the polymerization, the molded lens was slowlycooled, and then taken out from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.69, an Abbe's number ν_(d) of 32 and a heatdeformation start temperature of 154° C. Even when dyed in a dye bath at95° C., the lens was not deformed.

After dyeing, transmittances of the lens were 35% in the case ofML-Yellow, 38% in the case of ML-Red and 46% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.01%, and surface hardness was 2H.

Example 10

Mixed were 21 parts (0.11 mol) of bis(isocyanatomethylthio)methane, 25parts (0.068 mol) of4,8-bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol and 6.1 parts(0.027 mol) of isophorone diisocyanate to obtain a uniform solution, andthis solution was then sufficiently defoamed. Afterward, the solutionwas injected into a lens mold comprising a glass mold and a gasket. Insuccession, the solution was slowly heated from 30° C. to 120° C. over23 hours to achieve curing. After the completion of the polymerization,the molded lens was slowly cooled, and then taken out from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.68, an Abbe's number ν_(d) of 32 and a heatdeformation start temperature of 111° C. Even when dyed in a dye bath at95° C., the lens was not deformed.

After dyeing, transmittances of the lens were 30% in the case ofML-Yellow, 35% in the case of ML-Red and 46% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.01%, and surface hardness was H.

Example 11

Mixed were 26.0 parts (0.11 mol) of 1,2-bis(isocyanatomethylthio)ethane,19.5 parts (0.075 mol) of 1,2-bis(2-mercaptoethyl)thio!-3-mercaptopropane and 0.01% by weight (based onthe total amount of the mixture) of dibutyltin dilaurate to obtain auniform solution, and this solution was then sufficiently defoamed.Afterward, the solution was injected into a lens mold comprising a glassmold and a gasket which had been subjected to a release treatment. Insuccession, the solution was slowly heated from 40° C. to 120° C. over20 hours to achieve curing. After the completion of the polymerization,the molded lens was slowly cooled, and then taken out from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.66, an Abbe's number ν_(d) of 33 and a heatdeformation start temperature of 100° C.

After dyeing, transmittances of the lens were 30% in the case ofML-Yellow, 34% in the case of ML-Red and 43% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.04%, and surface hardness was H.

Example 12

Mixed were 22.0 parts (0.095 mol) of1,2-bis(isocyanatomethylthio)ethane, 14.0 parts (0.062 mol) of1,2,4-tris(mercaptomethyl)benzene and 0.01% by weight (based on thetotal amount of the mixture) of dibutyltin dilaurate to obtain a uniformsolution, and this solution was then sufficiently defoamed. Afterward,the solution was injected into a lens mold comprising a glass mold and agasket which had been subjected to a release treatment. In succession,the solution was slowly heated from 40° C. to 12° C. over 20 hours toachieve curing. After the completion of the polymerization, the moldedlens was slowly cooled, and then taken out from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.68, an Abbe's number ν_(d) of 31 and a heatdeformation start temperature of 122° C.

After dyeing, transmittances of the lens were 34% in the case ofML-Yellow, 39% in the case of ML-Red and 50% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.02%, and surface hardness was H.

Example 13

Mixed were 30.0 parts (0.12 mol) of 1,2-bis-(isocyanatoethylthio)ethane,16.7 parts (0.077 mol) of 1,2,4-tris(mercaptomethyl)benzene and 0.01% byweight (based on the total amount of the mixture) of dibutyltindilaurate to obtain a uniform solution, and this solution was thensufficiently defoamed. Afterward, the solution was injected into a lensmold comprising a glass mold and a gasket which had been subjected to arelease treatment. In succession, the solution was slowly heated from40° C. to 120° C. over 20 hours to achieve curing. After the completionof the polymerization, the molded lens was slowly cooled, and then takenout from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.67, an Abbe's number ν_(d) of 31 and a heatdeformation start temperature of 115° C.

After dyeing, transmittances of the lens were 32% in the case ofML-Yellow, 36% in the case of ML-Red and 45% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.03%, and surface hardness was H.

Example 14

Mixed were 40.0 parts (0.136 mol) of bis 2-(isocyanatomethylthio)ethyl!sulfide, 20.0 parts (0.057 mol) of 1,2,4-tris(mercaptomethyl)benzene and0.01% by weight (based on the total amount of the mixture) of dibutyltindilaurate to obtain a uniform solution, and this solution was thensufficiently defoamed. Afterward, the solution was injected into a lensmold comprising a glass mold and a gasket which had been subjected to arelease treatment. In succession, the solution was slowly heated from40° C. to 120° C. over 20 hours to achieve curing. After the completionof the polymerization, the molded lens was slowly cooled, and then takenout from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.67, an Abbe's number ν_(d) of 32 and a heatdeformation start temperature of 111° C.

After dyeing, transmittances of the lens were 33% in the case ofML-Yellow, 35% in the case of ML-Red and 43% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.04%, and surface hardness was H.

Example 15

Mixed were 39.2 parts (0.147 mol) ofbis(isocyanatomethylthio)phenylmethane, 25.5 parts (0.098 mol) of1,2-bis (2-mercaptoethyl)thio!-3-mercaptopropane and 0.01% by weight(based on the total amount of the mixture) of dibutyltin dilaurate toobtain a uniform solution, and this solution was then sufficientlydefoamed. Afterward, the solution was injected into a lens moldcomprising a glass mold and a gasket which had been subjected to arelease treatment. In succession, the solution was slowly heated from40° C. to 120° C. over 20 hours to achieve curing. After the completionof the polymerization, the molded lens was slowly cooled, and then takenout from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.68, an Abbe's number ν_(d) of 31 and a heatdeformation start temperature of 114° C.

After dyeing, transmittances of the lens were 35% in the case ofML-Yellow, 38% in the case of ML-Red and 49% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.04%, and surface hardness was H.

Example 16

Mixed were 22 parts (0.052 mol) of1,1,2,2-tetrakis(isocyanatomethylthio)ethane, 15.1 parts (0.07 mol) of1,2,4-tris(mercaptomethyl)benzene and 0.01% by weight (based on thetotal amount of the mixture) of dibutyltin dilaurate to obtain a uniformsolution, and this solution was then sufficiently defoamed. Afterward,the solution was injected into a lens mold comprising a glass mold and agasket which had been subjected to a release treatment. In succession,the solution was slowly heated from 40° C. to 120° C. over 20 hours toachieve curing. After the completion of the polymerization, the moldedlens was slowly cooled, and then taken out from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.70 and an Abbe's number ν_(d) of 30. A heatdeformation start temperature was not definitely confirmed until 200° C.After dyeing by the use of 2% benzyl alcohol as a carrier,transmittances of the dyed lens were 34% in the case of ML-Yellow, 42%in the case of ML-Red and 48% in the case of ML-Blue, and the totalevaluation of its dyeability was "o". After 48 hours, water absorptionwas 0.01%, and surface hardness was 2H.

Example 17

Mixed were 22 parts (0.052 mol) of1,1,2,2-tetrakis(isocyanatomethylthio)ethane and 19.3 parts (0.052 mol)of 4,8-bis(mercaptomethyl)-3,6,9-trithia-1,11-undecanedithiol to obtaina uniform solution, and this solution was then sufficiently defoamed.Afterward, the solution was injected into a mold comprising a glass moldand a gasket which had been subjected to a release treatment. Insuccession, the solution was slowly heated from 30° C. to 120° C. over23 hours to achieve curing. After the completion of the polymerization,the molded lens was slowly cooled, and then taken out from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.71 and an Abbe's number ν_(d) of 30. A heatdeformation start temperature was not definitely confirmed until 200° C.After dyeing by the use of 2% benzyl alcohol as a carrier,transmittances of the dyed lens were 29% in the case of ML-Yellow, 36%in the case of ML-Red and 45% in the case of ML-Blue, and the totalevaluation of its dyeability was "o". After 48 hours, water absorptionwas 0.01%, and surface hardness was 2H.

Example 18

Mixed were 21 parts (0.05 mol) of1,1,2,2-tetrakis(isocyanatomethylthio)ethane, 17.3 parts (0.067 mol) of1,2-bis (2-mercaptoethyl)thio!-3-mercaptopropane and 0.01% by weight(based on the total amount of the mixture) of dibutyltin dilaurate toobtain a uniform solution, and this solution was then sufficientlydefoamed. Afterward, the solution was injected into a lens moldcomprising a glass mold and a gasket which had been subjected to arelease treatment. In succession, the solution was slowly heated from40° C. to 120° C. over 20 hours to achieve curing. After the completionof the polymerization, the molded lens was slowly cooled, and then takenout from the mold.

The thus obtained lens was colorless and transparent and was excellentin impact resistance, and it had a refractive index n_(d) of 1.69, anAbbe's number ν_(d) of 31 and a heat deformation start temperature of179° C. After dyeing by the use of 2% benzyl alcohol as a carrier,transmittances of the dyed lens were 30% in the case of ML-Yellow, 37%in the case of ML-Red and 45% in the case of ML-Blue, and the totalevaluation of its dyeability was "o". After 48 hours, water absorptionwas 0.01%, and surface hardness was 2H.

Example 19

Mixed were 48.1 parts (0.092 mol) of2,2,5,5-tetrakis(isocyanatomethylthio)-1,4-dithiane, 26.7 parts (0.123mol) of 1,2,4-tris(mercaptomethyl)benzene and 0.01% by weight (based onthe total amount of the mixture) of dibutyltin dilaurate to obtain auniform solution, and this solution was then sufficiently defoamed.Afterward, the solution was injected into a lens mold comprising a glassmold and a gasket which had been subjected to a release treatment. Insuccession, the solution was slowly heated from 40° C. to 120° C. over20 hours to achieve curing. After the completion of the polymerization,the molded lens was slowly cooled, and then taken out from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.69, an Abbe's number ν_(d) of 31. A heatdeformation start temperature was not definitely confirmed until 200° C.After dyeing by the use of 2% benzyl alcohol as a carrier,transmittances of the dyed lens were 36% in the case of ML-Yellow, 41%in the case of ML-Red and 49% in the case of ML-Blue, and the totalevaluation of its dyeability was "o". After 48 hours, water absorptionwas 0.01%, and surface hardness was 2H.

Example 20

Mixed were 66.8 parts (0.128 mol) of2,2,5,5-tetrakis(isocyanatomethylthio)-1,4-dithiane, 44.5 parts (0.17mol) of 1,2-bis (2-mercaptoethyl)thio!-3-mercaptopropane and 0.01% byweight (based on the total amount of the mixture) of dibutyltindilaurate to obtain a uniform solution, and this solution was thensufficiently defoamed. Afterward, the solution was injected into a lensmold comprising a glass mold and a gasket which had been subjected to arelease treatment. In succession, the solution was slowly heated from40° C. to 120° C. over 20 hours to achieve curing. After the completionof the polymerization, the molded lens was slowly cooled, and then takenout from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.68, an Abbe's number ν_(d) of 31 and a heatdeformation start temperature of 170° C. After dyeing by the use of 2%benzyl alcohol as a carrier, transmittances of the dyed lens were 32% inthe case of ML-Yellow, 33% in the case of ML-Red and 44% in the case ofML-Blue, and the total evaluation of its dyeability was "o". After 48hours, water absorption was 0.01%, and surface hardness was 2H.

Comparative Example 1

Mixed were 25.3 parts (0.147 mol) of bis(2-isocyanatoethyl) sulfide and25.5 parts (0.098 mol) of 1,2-bis(2-mercaptoethyl)thio!-3-mercaptopropane to obtain a uniform solution,and this solution was then sufficiently defoamed. Afterward, thesolution was injected into a lens mold comprising a glass mold and agasket which had been subjected to a release treatment. In succession,the solution was slowly heated from 40° C. to 120° C. over 20 hours toachieve curing. After the completion of the polymerization, the moldedlens was slowly cooled, and then taken out from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.63, an Abbe's number ν_(d) of 36 and a heatdeformation start temperature of 106° C.

After dyeing, transmittances of the lens were 31% in the case ofML-Yellow, 33% in the case of ML-Red and 46% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.04%, and surface hardness was H.

In Comparative Example 1, the combination of the isocyanate having twoNCO groups and 1,2-bis (2-mercaptoethyl)thio!-3-mercaptopropane wasemployed, and when Comparative Example 1 is compared with Examples 8, 11and 15, it is apparent that refractive indexes of these examples are ashigh as 1.68, 1.66 and 1.68, respectively, but that of ComparativeExample 1 was low, 1.63.

Comparative Example 2

Mixed were 44 parts (0.16 mol) ofbis(isocyanatomethylthio)-(3-isocyanatopropyl)methane and 28 parts(0.107 mol) of 1,2-bis (2-mercaptoethyl)thio!-3-mercaptopropane toobtain a uniform solution, and this solution was then sufficientlydefoamed. Afterward, the solution was injected into a lens moldcomprising a glass mold and a gasket which had been subjected to arelease treatment. In succession, the solution was slowly heated from40° C. to 120° C. over 20 hours to achieve curing. After the completionof the polymerization, the molded lens was slowly cooled, and then takenout from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.65, an Abbe's number ν_(d) of 34 and a heatdeformation start temperature of 130° C.

After dyeing, transmittances of the lens were 45% in the case ofML-Yellow, 58% in the case of ML-Red and 58% in the case of ML-Blue, andthe dyeing was not accomplished and so the total evaluation of itsdyeability was "x". After the dyeing by the use of 2% benzyl alcohol asa carrier, the transmittances of the lens were 28% in the case ofML-Yellow, 31% in the case of ML-Red and 35% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.04%, and surface hardness was H.

In this Comparative Example 2, the combination of the isocyanate havingthree NCO groups and 1,2-bis (2-mercaptoethyl)thio!-3-mercaptopropane isemployed, but in the present invention, it is not required to use theisocyanate having three NCO groups. When the lens obtained inComparative Example 2 is compared with the lenses obtained in Examples8, 11 and 15 in which the combination of the isocyanate having two NCOgroups and 1,2-bis (2-mercaptoethyl)thio!-3-mercaptopropane is employed,it is apparent that the lens of Comparative Example 2 is more excellentin heat resistance but the lenses of the examples are more excellent inthe refractive index and the dyeability.

Furthermore, the lens of Comparative Example 2 is poor in both of therefractive index and the heat resistance, as compared with those of theexample of the isocyanate having four NCO groups (Example 18).

Comparative Example 3

Mixed were 33.9 parts (0.147 mol) of2,5-bis-(isocyanatomethyl)-1,4-dithiane and 25.5 parts (0.098 mol) of1,2-bis (2-mercaptoethyl)thio!-3-mercaptopropane to obtain a uniformsolution, and this solution was then sufficiently defoamed. Afterward,the solution was injected into a lens mold comprising a glass mold and agasket which had been subjected to a release treatment. In succession,the solution was slowly heated from 40° C. to 120° C. over 20 hours toachieve curing. After the completion of the polymerization, the moldedlens was slowly cooled, and then taken out from the mold.

The thus obtained lens was colorless and transparent and had arefractive index n_(d) of 1.67, an Abbe's number ν_(d) of 33 and a heatdeformation start temperature of 126° C.

After dyeing, transmittances of the lens were 35% in the case ofML-Yellow, 35% in the case of ML-Red and 46% in the case of ML-Blue, andthe total evaluation of its dyeability was "o". After 48 hours, waterabsorption was 0.04%, and surface hardness was H.

In this Comparative Example 3, the combination of 1,2-bis(2-mercaptoethyl)thio!-3-mercaptopropane and the isocyanate having a1,4-dithiane ring and two NCO groups is employed, but since thisisocyanate has the dithiane ring, a refractive index and heat resistanceequal to those of the present invention can be imparted to the lens,though the compound has two NCO groups. However, as compared withExample 20 in which the isocyanate having the same dithiane ring isused, the lens of Comparative Example 3 is noticeably poor.

As described above, according to the present invention, a specificpolyisocyanate is used, whereby optical materials such as plastic lenseshaving a very high refractive index and heat resistance can be provided.

What is claimed is:
 1. A polyisocyanate represented by the followingformula (4): ##STR9## wherein Z is any one of the following groups;

    --CH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 --, ##STR10## B' is --CH.sub.2 -- or --CH.sub.2 CH.sub.2 ; and n is an integer of 2 or
 4.


2. The polyisocyanate according to claim 1 wherein the polyisocyanate isbis 2-(isocyanatomethylthio)ethyl! sulfide represented by the followingformula (6):

    OCNCH.sub.2 SCH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 SCH.sub.2 NCO(6).


3. The polyisocyanate according to claim 1 wherein the polyisocyanate isbis(isocyanatomethylthio)phenylmethane represented by the followingformula (7): ##STR11##
 4. The polyisocyanate according to claim 1wherein the polyisocyanate is1,1,2,2-tetrakis(isocyanatomethylthio)ethane represented by thefollowing formula (8): ##STR12##
 5. The polyisocyanate according toclaim 1 wherein the polyisocyanate is2,2,5,5-tetrakis(isocyanatomethylthio)-1,4-dithiane represented by theformula (9): ##STR13##